The present invention relates in general to spinal fixation systems and in particular to facet screw systems for securing adjacent facet joints together.
Facet screws are used to secure a patient""s facet joints together, thus preventing relative movement between adjacent facet joints. Such facet screws are typically used during various spinal surgery procedures such as discectomy with posterior instability; degenerative disc disease; degenerative joint disease in the facet joint; and general instability, both to prevent relative movement of the facet joints (thus promoting arthrodesis) and to provide support and stability to the vertebral level (thus promoting arthrodesis).
Other benefits of facet joint screws are that they can be used to stabilize the spine in lieu of more expensive and surgically time consuming instrumentation, for example, pedicle screw systems.
A common disadvantage with existing facet screw systems are that they must be used in conjunction with other stabilization systems, for example, anterior strut grafts or other inorganic implants, to provide sufficient stability to the patient""s vertebrae after surgery and also that they require a difficult surgical procedure to safely place them.
The present invention provides systems for securing a pair of facet joints together. An advantage of the present invention is that by immobilizing opposing adjacent facet joints with respect to one another it provides stability for vertebral arthrodesis, as is desired, for example, after a medical procedure such as a discectomy with fusion.
In accordance with the present invention, a system is provided to position a facet screw to secure a patient""s opposite adjacent first and second facet joints together, and to promote fusion therebetween.
In a preferred aspect, the facet screw is positioned to secure together the inferior articular process of the first facet joint and the superior articular process of the second facet joint, with the facet screw positioned to pass from a posterior approach through the first facet joint toward the pedicle of the second facet joint. This embodiment is called the transfacet approach. Other approaches for facet screw placement are also contemplated (i.e. the translaminar approach).
In a preferred aspect of the present invention, the contacting surfaces of the adjacent facet joints are ablated (to promote fusion) prior to the facet screw being inserted (to securely hold the facet joints together). An advantage of the present system of ablation is that it utilizes the natural healing response of the facet bones, where the ablated contacting surfaces of the facet joints will tend to fuse together after such ablation.
In a preferred aspect of the present invention, the opposite contacting surfaces of the facet joints are ablated by an extending member which protrudes radially outwardly from a drill (at a location between the opposite contacting surfaces). Preferably, the drill from which the extending member protrudes is the same drill which is used to drill a hole for the facet screw placement.
Most preferably, the extending member comprises a flexible wire which is received in a cannulated passageway in the drill. In this preferred aspect of the invention, the drill preferably has a side hole and the extending member (i.e.: the flexible wire) is advanced distally through a cannulated passage in the drill such that the wire""s distal end protrudes radially outwardly through the side hole in the drill.
In this aspect of the invention, the drill is advanced through the first facet joint and into the second facet joint to a depth such that it""s side hole is positioned between the opposite contacting surfaces of the first and second facet joints.
Thereafter, the extending member is advanced to protrude outwardly to a desired radial distance from the drill, such that further rotation of the drill will cause the extending member to rotate in a circular path around the drill, thereby ablating a rather large surface area of the opposite contacting surfaces of the first and second facet joints. The specific size of the ablated region on each of the opposite contacting surfaces on the first and second facet joints will depend upon the length to which the distal end of the extending member is advanced to protrude outwardly from the drill.
Accordingly, an advantage of the present drill being adapted such that an extending member can be deployed therefrom (e.g.: through a side hole therein) is that a rather large area of the facet joint surfaces can be accessed and thereby ablated, yet requiring only a standard sized drill hole as would typically be used to insert a standard facet screw.
In optional aspects of the present invention, the facet screw is introduced into the patient in a cannulated posterior approach. In such aspects of the invention, the drill may be advanced through an operating cannula such that a distal end of the drill commences drilling at a posterior point on the inferior articular process of the first facet joint.
In yet another optional aspect of the present invention, the drill itself is dimensioned (i.e.: tapered) to drill a countersink into the first facet joint, such that the head of the facet screw can be received substantially flush against the first facet joint. Consequently, the head of the facet screw can be positioned out of the way of surrounding tissues.
In yet another optional aspect of the present invention, the drill (and the facet screw) are positioned in a preferred posterior approach into the patient by way of a surgical guidance platform, with the drill and the facet screw being sequentially advanced through an operating cannula which is supported by the surgical guidance platform.
In yet another optional aspect of the present invention, the extending member is advanced into the facet joint between the opposing contact surfaces of the first and second facet joints by means of a cannulated delivery device (rather than a drill).
In an optional preferred aspect of the present invention, the extendible member may comprise a wire made of a shape memory metal, such as Nitinol, but is not so limited as other suitable materials may instead be used.